Presentation on theme: "Darwin’s Theory of Evolution"— Presentation transcript:
1 Darwin’s Theory of Evolution Chapter 16Darwin’s Theory of Evolution
2 Chapter 16 Mystery SUCH VARIED HONEYCREEPERS Page 449… Hypothesis: How did all these birds get to Hawaii? How did some of them come to have such specialized diets?
3 Section 16.1 Darwin’s Voyage of Discovery Objectives:What was Charles Darwin’s contribution to science?What three patterns of biodiversity did Darwin note?Define:EvolutionFossil
4 I. Darwin’s Epic Journey Charles Darwin – England – 1809Evolution – process of change over timeDarwin developed a scientific theory of biological evolution that explains how modern organisms evolved over long periods of time through descent from common ancestors1831 – HMS Beagle – 5 year voyage – map coastline of SADarwin planned to collect specimens of plants and animalsDarwin’s work = vital insights into today’s world by showing how living world is constantly changing helps us understand modern phenomena (drug-resistant bacteria & newly emerging diseases like avian flu)
5 II. Observations Aboard the Beagle 1 day – Brazilian forest = 68 species of beetles (when he wasn’t particularly looking for beetles)Observed characteristics & habitsKept eyes and mind open to larger patterns into which observations might fit3 distinct patterns:Species vary globallySpecies vary locallySpecies vary over time
6 A. Species Vary Globally SA, Australia, AfricaDarwin noticed that different, yet ecologically similar, animal species inhabited separated, but ecologically similar habitats around the globe.Rhea – flightless, ground-dwelling bird SAOstrich – same characteristics AfricaEmu – same characteristics AustraliaRabbits in Eur. grasslands, but not in SAKangaroos only in Aus.
7 B. Species Vary LocallyDarwin noticed that different, yet related, animal species often occupied different habitats within a local area2 species of rhea (SA) – 1 in grassland & 1 in colder, harsher scrublandGalapagos Islands – close to each other but different ecological conditionsDistinct forms of giant land tortoises (shells varied from one island to another)Different islands = different varieties of mockingbirds (all resembled mockingbirds in SA) beaks w/ different shapes (wrens, warblers, blackbirds)
8 Mystery CluePage 452…Like the small brown birds on the Galapagos, Hawaiian honey creepers live on islands with slightly different habitats.How might these varied habitats have affected the evolution of honeycreeper species
9 C. Species Vary Over Time Darwin also collected fossilsFossil – preserved remains or traces of ancient organismsSome looked like current living organisms, but some looked nothing like current living organismsDarwin noticed that some fossils of extinct animals were similar to living speciesGlyptodont – giant armored animal found in area where current armadillo is foundArmadillo = smaller version of glyptodont
10 D. Putting the Pieces of the Puzzle Together Mockingbirds = 3 species of finches found nowhere elseWren, warbler, blackbirds = all species of finches found nowhere elseTortoises, marine iguanas, plants = only on GalapogosDid these species evolve from SA species?Suggested: species are not fixed & can change by some natural process
11 Section 16.2 Ideas that Shaped Darwin’s Theory Objectives:What did Hutton and Lyell conclude about Earth’s history?How did Lamarck propose that species evolve?What was Malthus’s view of population growth?How is inherited variation used in artificial selection?Define:Artificial selection
12 I. An Ancient, Changing Earth People thought: Earth was few 1000 yrs old & didn’t change muchHutton and Lyell concluded that the Earth is extremely old and that the processes that changed Earth in the past are the same processes that operate in the present1785 – Hutton presented infoLyell – built on Hutton – Principles of Geology
13 A. Hutton and Geological Change Recognized connections b/w geological processes and geological features (mountains, valleys, folded layers of rock)Some rocks form from lava & some form from layers of sedimentProposed force beneath surface can push rock layers upward = mountain rangesWorn down by rain, wind, heat & coldProcesses = v. slow so Earth must be much olderDeep time – idea that our planet’s history stretches back over a period of time so long that it is difficult to imagine
14 B. Lyell’s Principles of Geology Laws of nature = constant over timeUniformitarianism – geological processes we see today must be same ones that shaped Earth myaAncient volcanoes released gases & lavaAncient rivers dug channels (canyons & valleys)Darwin uses Lyell’s insightsEarthquake raised shoreline 3m out of seaCould be how Andes mountains formedExplains how fossils of marine animals could be found at tops of mountains
15 II. Lamarck’s Evolutionary Hypothesis Jean Baptiste Lamarck – proposed theory of evolution based on growing fossil recordLamarck suggested that organisms could change during their lifetimes by selectively using or not using various parts of their bodies.He also suggested that individuals could pass these acquired traits onto offspring, enabling species to change over timePublished ideas in 1809 – year Darwin was born
16 A. Lamarck’s IdeasProposed all organisms have inborn urge to become more complex and perfectAs a result organisms change and acquire features that help them live more successfully in environmentsOrgs. can change size/shape of organs by using bodies in new waysExample: waterbird = long legsStructures of orgs. could change if not usedExample: bird stopped using wings = smaller wingsAcquired characteristics – traits altered by an org during its lifeInheritance of acquired characteristics – traits acquired during lifetime can be passed on to offspring
17 B. Evaluating Lamarck’s Hypothesis Lamarck was Incorrect b/c:Orgs do not have inborn drive to be perfectEvolution does not mean that over time species becomes “better” somehowEvolution does not progress in predetermined directiontraits acquired by orgs during lifetime cannot be passed on to offspringLamarck was one of 1st to try to explain evolution scientifically using natural processesRecognized link b/w org’s environment and body structures
18 III. Population Growth1798 – Thomas Malthus – humans were being born faster than they were dying = overcrowdingMalthus reasoned that if human population grew unchecked, there wouldn’t be enough living space and food for everyoneForces that work against pop growth = war, famine, diseaseDarwin applied to other orgs (maple tree, oyster)Darwin realized most organisms don’t survive and reproduce… wondered which individuals survived and why
19 IV. Artificial Selection Darwin studied change produced by plant and animal breedersBreeders knew that indiv. orgs. vary: some bear larger/smaller fruit than other species & some cows bear more/less milk than others in same herdTold Darwin that some of this variation could be passed from parent to offspring (used to improve crops/livestock)Artificial selection – nature provides the variation and humans select those they find useful & allow them to reproduce to produce offspring with similar traitsDarwin recognized natural variation was v. impt b/c provided raw material for evolution
20 Section 16.3 Darwin Presents His Case Objectives:Under what conditions does natural selection occur?What does Darwin’s mechanism for evolution suggest about living and extinct species?Define:AdaptationFitnessNatural selection
21 I. Evolution by Natural Selection Evolution is a Scientific mechanismOn the Origin of SpeciesCombined ideas of his own with Lamarck and Malthus
22 A. Struggle for Existence If more individuals are produced than can survive members of a population must compete to obtain food, living space, and other limited necessities of lifeCalled: Struggle for ExistenceWhich individuals come out on top of struggle?
23 B. Variation and Adaptation Individuals have natural variations among heritable traitsSome variants are better suited to life in their environment than othersPredatory species that are faster, longer claws, sharper teeth catch more preyPrey species that are faster, better camouflaged avoid being caughtAdaptation – any heritable characteristic that increases an org’s ability to survive and reproduce in its environmentBody parts or structures (tiger’s claws, camouflage)Physiological functions (photosynthesis)Behaviors (complex avoidance strategies of prey)
24 C. Survival of the Fittest Differences in adaptations affect an indiv’s fitnessFitness – how well an org can survive and reproduce in its environmentHigh fitness – well suited to env; can survive & reproduceLow fitness – not well suited to env die w/o reproducing or leave few offspringSurvival of the fittest – difference in rates of survival and reproductionSurvival – means more than living; must also reproduce and pass on adaptations to next generation
25 D. Natural SelectionNatural selection – mechanism for evolution - process by which orgs w/ variations most suited to local env survive and leave more offspringOnly certain indivs in population produce new indivsFitness determined by environmentNatural selection occurs in any situation in which more individuals are born than can survive (struggle for existence), there is natural heritable variation (variation and adaptation), and there is variable fitness among indivs (survival of fittest).Well adapted indivs survive and reproducePopulations continue to change as they become better adapted or as env changesNatural selection acts only on inherited traits b/c those are the only chars that parents can pass onto offspring
26 Natural selection does not make orgs “better” Adaptations don’t have to be perfect – just good enough to enable org to pass its genes to next generationdoesn’t have to move in fixed direction – no one perfect way of doing somethingIf local env changes traits that were once adaptive may no longer be useful and different traits may become adaptiveIf env changes faster than species can adapt = extinct
27 Mystery CluePage 463…How might natural selection explain the history of the Hawaiian honeycreepers?
28 II. Common DescentNatural selection depends on ability of orgs to reproduceEvery org alive today is descended from parents who survived and reproducedWell-adapted indivs in species survived and reproduce well adapted species survive over timeLiving species are descended with modification from common ancestors (descent with modification)Implies life has been on Earth for v. long timeHutton & Lyell – deep time gave enough time for natural selection to occurUsed fossil record for evidence
29 “Tree Thinking” – implies that all organisms are related Darwin based explanation for diversity of life on idea that species change over time“Tree Thinking” – implies that all organisms are relatedCommon ancestor shared by tigers, panthers, cheetahsCommon ancestor shared by these felines and horses, then batsFarther back all mammals share ancestor with birds, alligators, fishAccording to the principle of common descent, all species – living and extinct – are descended from common ancestors
30 Section 16.4 Evidence of Evolution Objectives:How does the geographic distribution of species today relate to their evolutionary history?How do fossils help to document the descent of modern species from ancient ancestors?What do homologous structures and similaritiesDefine:BiogeographyHomologous structureAnalogous structureVestigal structure
31 I. BiogeographyBiogeography – study of where orgs live now and where they and their ancestors lived in the pastPatterns in the distribution of living and fossil species tell us how modern orgs evolved from their ancestorsPattern in which closely related species differentiate in slightly different climatesPattern in which very distantly related species develop similarities in similar environments
32 A. Closely Related but Different Biogeography of Galapagos species suggested that population on island evolved from mainland speciesOver time natural selection on islands produced variations among populationsResulted in different but closely related island speciesWeevilsCottonWaspsBeetleSnakesScorpionFinches
33 B. Distantly Related but Similar Similar habitats around world often home to animals and plants that are only distantly relatedSimilar ground-dwelling birds inhabit similar grasslands in Europe, Aus, AfricaDifferences in body structures among those animals provide evidence that they evolved from different ancestorsSimilarities among those animals provide evidence that similar selection pressures caused distantly related species to develop similar adaptations
34 Mystery CluePage 465…How can biogeography help explain why some species of honeycreepers are found only on the Hawaiian Islands?
35 II. The Age of Earth and Fossils 2 potential difficultiesage of EarthGaps in fossil record
36 A. The Age of Earth50 yrs after Darwin physicists discovered radioactivityGeologists use radioactivity to establish age of certain rocks and fossilsRadioactive dating indicates that Earth is ~4.5 billion years oldThis is plenty of time for natural selection to take place
37 B. Recent Fossil Finds“imperfection of geological record” – 1859 – paleontologists had not found enough fossils of intermediate forms of life to document evolution of modern species from their ancestorsMany recently discovered fossils form series that trace evolution of modern species from extinct ancestorsSince Darwin paleontologists have discovered hundreds of fossils that document intermediate stages in evolution of many different groups of modern speciesWhales from ancient land mammalsDinosaurs & birdsFish & four-legged land animals
38 II. Comparing Anatomy and Embryology All vertebrate limbs have same basic bone structureSome were used for crawling, some for climbing, some for running, others for flying
39 A. Homologous Structures Darwin proposed animals w/ similar structures evolved from common ancestor w/ basic version of that structureHomologous structures – structures shared by related species and have been inherited from common ancestorEvolutionary theory explains existence of homologous structures adapted to different purposes as result of descent with modification from a common ancestorBiologists test whether structures are homologous by studying anatomical details, way structures develop in embryos, pattern in which they appeared over evolutionary historySimilarities and differences among homologous structures help determine how recently species shared a common ancestorCommon ancestor to all four-limbed animals = ancient lobe-finned fish (380 mya)Also some plants have homologous roots, stems, flowers
40 1. Analogous Structures Clue to common descent = common structure Not common functionAnalogous structures – body parts that share common function but not structureExample: wing of bee and wing of bird
41 2. Vestigial StructuresVestigial structures – inherited from ancestors but have lost much or all of their original function due to different selection pressures acting on descendantExample: hipbones of bottlenose dolphinPresence does not affect organism’s fitness so natural selection does not act to eliminate it
42 B. EmbryologyEarly developmental stages of many animals with backbones (vertebrates) look very similarSame groups of embryonic cells develop in same order and in similar patterns to produce many homologous tissues and organs in vertebratesSimilar patterns of embryological development provide further evidence that organisms have descended from a common ancestor
43 III. Genetics and Molecular Biology Darwin had no idea how heredity workedSome of most impt evidence for theory comes from geneticsAt molecular level, universal genetic code and homologous molecules provide evidence of common descentAlso: we now understand how mutation and reshuffling of genes during sexual reproduction produce heritable variation on which natural selection operates
44 A. Life’s Common Genetic Code All living cells use info coded in DNA and RNA to carry info from one generation to next and to direct protein synthesisGenetic code is nearly identical in almost all orgs (bacteria, yeasts, plants, fungi, animals)ALL ORGS EVOLVED FROM COMMON ANCESTORS THAT SHARED THIS CODE
45 B. Homologous Molecules Homology not limited to physical structuresHomologous proteins – share extensive structural and chemical similaritiesExample: cytochrome c – cellular respiration – found in almost all living cellsHomologous genes – makes sense b/c all animals share same codeExample: Hox genes – determine head-to-tail axis in embryonic development – found in almost all multicellular animalsLIVING ORGS EVLOVED THROUGH DESCENT WITH MODIFICATION FROM A COMMON ANCESTOR
46 IV. Testing Natural Selection To gather evidence observe natural selection in progressEvolutionary change takes place over millions of years tough to see change actually happeningSome have been observed and studied in labs and controlled outdoor environmentsBacteria, guppiesResults support Darwin’s basic ideasBest examples of natural selection in action comes from observations on animals living in natural environment: Galapagos finches
47 A. A Testable Hypothesis Galapagos finches – darwin thought they were wrens, warblers, and blackbireds b/c looked so differentOnce he learned all finches, he hypothesized: descended from common ancestorBeaks: different size and shapes – used to pick up and eat different foods natural selection shaped beaks as became adapted to eat different foods
48 Peter and Rosemary Grant – Princeton Darwin’s theory rested on 2 testable assumptions:For beak size and shape to evolve, there must be enough hertiable variation in those traits to provide raw material for natural selectionDifferences in beak size and shape must produce differences in fitnessCaught and tagged each of one species on one island recaught to see which lived and reproducedEach individual bird recorded anatomical characteristics (wing length, leg length, total mass, beak length, beak depth, beak color, feather color)Showed great variation among finches
49 B. Natural SelectionIndividual finches w/ different-size beaks have better or worse chances of surviving both seasonal droughts and longer dry spellsfood scarce birds w/ largest beaks – more likely to surviveResult: average beak size in finch population has increased dramaticallyThe Grants have documented that natural selection takes place in wild finch populations frequently, and sometimes rapidlyChanges in food supply created selection pressure that caused finch populations to evolve w/in decadesOccurred much faster than many researchers thought possible
50 Grants documented natural selection in nature Their data also confirm that competition and environmental change drive natural selectionTraits that don’t matter much under one set of environmental conditions became adaptive as environment changes during a droughtThe Grants’ work shows that variation within a species increases the likelihood of the species’ adapting to and surviving environmental changeWithout heritable variation in beak sizes, the medium ground finch would not be able to adapt to feeding on larger tougher seeds during a drought
51 C. Evaluating Evolutionary Theory Advances in fields of biology & other sciences confirmed and expanded most of Darwin’s hypothesesEvolutionary theory – includes natural selection – offers insights that are vital to all branches of biologyEvolution often called unifying theory of the life sciencesConstantly reviewed as new data is gatheredDebate questions (how new species arise and why species become extinct)Uncertainty about exactly how life beganQuestions remain about how evolution works; not whether evolution occursTo scientists, evolution is key to understanding natural world
52 Solve the Mystery Page 477…. Suppose a small group of birds, not unlike the modern honeycreepers, landed on one of Hawaii’s islands millions of years ago and then reproduced. Do you think all the descendants would have stayed on that one island? Explain.Do you think that the climate and other environmental conditions are exactly the same everywhere on the Hawaiian Islands? How might environmental conditions have affected the evolution of honeycreeper species?Explain how the different species of honeycreepers in Hawaii today might have evolved from one ancestral species.Why are islands often home to species that exist nowhere else on Earth?
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